Writing our own vows

Hi everyone!

For those who have been married at Couples, or who understand more about what will happen at the ceremony, can we write our own vows? I know the Couples official stance is that you can add your own "short exchange," but what does that mean? I want to make sure whatever I write isn't too long or involved. Do any of you guys have examples of what you used? That would be SO helpful. Thank you!